Department of Laboratory Medicine and Pathobiology, Temerty Faculty of Medicine, University of Toronto, Toronto, ON M5G 1M1, Canada
Audrey Astori
Princess Margaret Cancer Centre, University Health Network, Toronto, ON M5G 1L7, Canada
Nevraj S. Kejiou
Department of Biochemistry, Temerty Faculty of Medicine, University of Toronto, Toronto, ON M5G 1M1, Canada
Chris A. Jordan
Department of Laboratory Medicine and Pathobiology, Temerty Faculty of Medicine, University of Toronto, Toronto, ON M5G 1M1, Canada
Negin Khosraviani
Department of Laboratory Medicine and Pathobiology, Temerty Faculty of Medicine, University of Toronto, Toronto, ON M5G 1M1, Canada
Janet N.Y. Chan
Department of Laboratory Medicine and Pathobiology, Temerty Faculty of Medicine, University of Toronto, Toronto, ON M5G 1M1, Canada
Razqallah Hakem
Department of Laboratory Medicine and Pathobiology, Temerty Faculty of Medicine, University of Toronto, Toronto, ON M5G 1M1, Canada; Princess Margaret Cancer Centre, University Health Network, Toronto, ON M5G 1L7, Canada; Department of Medical Biophysics, Temerty Faculty of Medicine, University of Toronto, Toronto, ON M5G 1L7, Canada
Brian Raught
Princess Margaret Cancer Centre, University Health Network, Toronto, ON M5G 1L7, Canada; Department of Medical Biophysics, Temerty Faculty of Medicine, University of Toronto, Toronto, ON M5G 1L7, Canada
Alexander F. Palazzo
Department of Biochemistry, Temerty Faculty of Medicine, University of Toronto, Toronto, ON M5G 1M1, Canada
Karim Mekhail
Department of Laboratory Medicine and Pathobiology, Temerty Faculty of Medicine, University of Toronto, Toronto, ON M5G 1M1, Canada; Corresponding author
Summary: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) hinders host gene expression, curbing defenses and licensing viral protein synthesis and virulence. During SARS-CoV-2 infection, the virulence factor non-structural protein 1 (Nsp1) targets the mRNA entry channel of mature cytoplasmic ribosomes, limiting translation. We show that Nsp1 also restrains translation by targeting nucleolar ribosome biogenesis. SARS-CoV-2 infection disrupts 18S and 28S ribosomal RNA (rRNA) processing. Expression of Nsp1 recapitulates the processing defects. Nsp1 abrogates rRNA production without altering the expression of critical processing factors or nucleolar organization. Instead, Nsp1 localizes to the nucleolus, interacting with precursor-rRNA and hindering its maturation separately from the viral protein’s role in restricting mature ribosomes. Thus, SARS-CoV-2 Nsp1 limits translation by targeting ribosome biogenesis and mature ribosomes. These findings revise our understanding of how SARS-CoV-2 Nsp1 controls human protein synthesis, suggesting that efforts to counter Nsp1’s effect on translation should consider the protein’s impact from ribosome manufacturing to mature ribosomes.
